Among the gallery of proton conductors are solid heteropolyacids, e.g., polyoxometalates. However, because they are solid, they are highly sensitive to temperature and humidity.
Moreover known functionalized nanoparticles in the absence of solvent behave solid-like. Solids present environmental concern and require presence of solvents for films and functional fluids.
Furthermore layered organic-inorganic hybrids including nanoclays have potential application as rheology control additives and in nanocomposites. However, they do not reversibly melt (undergo a solid-to-liquid transition) at low temperatures; they are not useful therefore as lubricants, plasticizers or film forming precursors.
In each case, the disadvantage is that a compound with an inorganic component does not undergo solid-to-liquid phrase transition at low temperature, i.e., demonstrate liquid-like behavior at low temperature.